1. Field
Disclosed herein is a current sensor arrangement with a magnetic module, in particular for use as a compensation current sensor.
2. Description of Related Art
In the non-contact measurement of current, first and foremost current sensors are used, in which the magnetic field, which is produced by a current (primary current) that is to be measured and that flows through a so-called primary conductor, is evaluated, and the current that actually flows into the primary conductor is determined therefrom. Current sensors that operate without contact, i.e., that have no galvanic contact with the primary conductor, are primarily used with high currents.
Current sensors can be configured in a variety of ways, in particular with respect to the magnetic field sensors and magnetic modules that are used there. Magnetic field sensors are mainly sensor types that operate inductively or based on the Hall Effect. To bundle or to conduct the magnetic field, soft-magnetic elements (e.g., magnetic cores) are used, which are a minimum component of a magnetic module.
For example, in the so-called compensation current sensors, in which the magnetic field that is produced by the primary current is compensated to zero by a magnetic field that is produced by a compensation current of known strength, a magnetic core of closed structure, such as, for example, a circular or rectangular ring structure, is used as a soft-magnetic element, whereby an air gap is provided for receiving a magnetic field probe. By means of the magnetic field probe, the residual magnetic field, which is what remains in this case incomplete compensation, is measured, and the compensation current is correspondingly readjusted. In this case, the compensation current is a measurement for the primary current. In particular, in the measurement of higher electrical currents, for example above 500 A, however, various problems occur.
For example, primary conductors in the case of high currents have a correspondingly large cross-section. In the case of compensation current sensors for high currents, to keep the overall dimensions of the magnetic module as small as possible, the geometry of the inside opening of the magnetic module that accommodates the primary conductor should be selected in such a way that the free space between the magnetic module and the primary conductor is as small as possible. However, the primary conductors can have both round and rectangular cross-sections, so that the magnetic modules can be optimized only for a primary conductor cross-section in each case, and other primary conductor cross-sections cannot be used or can be used only with limitations.
If the magnetic module, for example, has a rectangular inside opening, for example for receiving a strip-like conductor, then only two sides of the core can generally be provided with windings; this limits the possible measuring area and the non-linearities of the current sensor, by which in turn falsifications of the measuring outcome (measuring errors) are produced. When a circular, uniformly wound single-aperture core is used, this is not a problem, but the winding expense is increased in this case and thus the total price is increased considerably, whereby, moreover, measurements can be made on a primary conductor with a rectangular cross-section with a given single-aperture core with a round inside opening only with a reduced cross-sectional surface of the conductor and thus with a reduced maximum primary current.
Another problem consists in the fact that magnetic modules in higher primary currents and thus accompanying larger cross-sectional surfaces of the primary conductor require a sensor core of corresponding size to be able to guide the “larger” primary conductor through the inside opening. As the primary current increases, moreover, the effects of an asymmetrical magnetic modulation of the core are magnified, when, for example, the position of the electric conductor is not secure in the inside opening and partial saturations of the magnetic module then occur. Non-linearities and thus measuring errors can be caused by such saturations.
Since even though in a conventional compensation current sensor, the magnetic field in the air gap is kept essentially to zero, relatively large magnetic fields can occur at other areas of the magnetic core since compensation current and primary current are not compensated there because of stray flux. This results in large measuring errors, which thus far have been counteracted by large core cross-sections.